The present invention relates generally to an antenna for transmitting to and receiving signals from one or more transmitting and receiving sources such as satellites, wherein the received signals are dual-polarized such that they simultaneously contain two components of different polarizations such as two different linearly polarized components on orthogonal planes, or right-hand and left-hand circularly polarized components.
In recent years, there has been a significant increase in the amount and types of information that is transmitted via satellite communication. For instance, satellites now transmit telephone signals, television signals, internet data, etc. Due to the expanded use of satellites for data communication, there has also been an associated increase in the number of satellites placed in orbit about the earth. For instance, there are currently satellites that are dedicated to transmission of not only television signals in general, but are dedicated to transmission of only certain types of programming, such as movie channels, foreign language channels, local channel programming, or high definition television signals. Satellites have also been deployed for the transmission of internet signals for some internet providers.
As the use of satellite communications continues to increase, there is a general trend toward more widespread use of satellite antennas by private individuals and commercial and governmental users. For these types of applications, cost and aesthetics are major concerns in the design of antennas. Providing a low cost, compact, and aesthetically pleasing antenna, however, presents design challenges.
One such challenge is reducing the overall size of an antenna while at the same time providing increased functionality required by changes in the way data communications with satellites are conducted. More particularly, there is a trend in satellite communications toward greater and greater utilization of xe2x80x9cfrequency reusexe2x80x9d so that increasing amounts of information can be transmitted and received within a given frequency band. Frequency reuse refers to a method of increasing the throughput of information in a frequency band by dual-polarizing a transmitted signal such that the signal contains two components of different polarizations. For instance, two components can be linearly polarized in two different planes, typically orthogonal to each other and usually referred to as xe2x80x9cverticalxe2x80x9d and xe2x80x9chorizontalxe2x80x9d planes. Alternatively, both right-hand and left-hand circularly polarized components can be contained in the same signal. In either case, each component is encoded with information, such that about half of the transmitted information is carried in one polarization component and the other half is carried in the other polarization component. Traditionally, in the satellite antenna industry, such dual-polarized signals containing vertical and horizontal linearly polarized components have been received by a transmit/receive (T/R) feed and passed through an ortho-mode transducer (OMT), which is essentially a Y junction that channels transmitted signals from a transmitter of the antenna to the T/R feed, and channels received signals received by the T/R feed to a receive side of the antenna. The receive side of the antenna traditionally has included a diplexer for separating the vertical polarization component of the received signal from the horizontal component thereof. Downstream of the diplexer, a pair of rectangular waveguide/filter elements have traditionally been used for separately filtering the vertical and horizontal components of the received signal so as to prevent signals transmitted by the transmitter of the antenna from propagating down the receive side of the antenna to the antenna""s receiver. After the vertical and horizontal components are separately filtered, they are typically recombined in a recombiner, and are then passed to further electronics for processing before being passed to the antenna""s receiver. Thus, the conventional antenna capable of handling dual-polarized signals has required a diplexer, two separate filter elements, and a recombiner. All of these components can add to the cost and overall size of the antenna.
The present invention addresses the above-noted needs by providing an apparatus for receiving signals from and transmitting signals to a source such as a satellite, in which the traditionally used diplexer, separate vertical and horizontal filters, and recombiner are replaced by a considerably simplified system for handling dual-polarized received signals. In accordance with one preferred embodiment of the invention, the apparatus comprises a transmit/receive feed operable to transmit signals to and receive signals from a source, a waveguide assembly coupled with the transmit/receive feed for propagating transmitted and received signals to and from the transmit/receive feed, and a receive isolation filter coupled with the waveguide assembly and operable to filter the dual-polarized received signals without separating the two components thereof and to provide the filtered dual-polarized received signals to a receiver so as to isolate the receiver from signals transmitted by the transmit/receive feed. Thus, both components of the received signals are filtered simultaneously along the same path of propagation, eliminating the need to split the components along separate paths, separately filter them, and then recombine them as in prior antennas. The receive isolation filter, also referred to herein as a dual-mode filter, can filter signals containing two orthogonal linearly polarized components, and can also filter signals containing right-hand and left-hand circularly polarized signals.
The apparatus in accordance with the invention preferably forms a part of an antenna for receiving signals from and transmitting signals to a satellite. In a preferred embodiment, the receive isolation filter defines multiple internal cavities of different dimensions. In order to simultaneously filter two orthogonal components of the dual-polarized received signals, the receive isolation filter preferably defines an internal waveguide passage that has 90xc2x0 rotational symmetry about its longitudinal axis. By xe2x80x9c90xc2x0 rotational symmetryxe2x80x9d is meant that a cross-section through the passage along a first plane, such as the plane of one of the polarization components and containing the longitudinal axis of the passage, is substantially identical to a cross-section through the passage along a second plane orthogonal the first plane and also containing the longitudinal axis. Thus, the passage appears the same to each of the polarization components, whether the components comprise two orthogonal linearly polarized components or right-hand and left-hand circularly polarized components. In other words, the filter is polarization-independent. Various internal cross-sectional shapes having such 90xc2x0 rotational symmetry can be used for the filter, including but not limited to circular cylindrical passages or square passages. In a preferred embodiment, the receive isolation filter has a circular internal cross-section. More particularly, in a preferred embodiment the receive isolation filter comprises a plurality of sequentially arranged circular cylindrical cavities of different internal diameters and volumes.
The apparatus can be incorporated in an antenna for communications with two different sources such that the antenna transmits to and receives from a first source and only receives from a second source. In this case, the apparatus also includes a second feed operable to receive signals from the second source, and a second receive isolation filter operable to filter the received signals from the second feed so as to isolate the antenna""s receiver from signals transmitted by the transmit/receive feed. Of course, if the signals received by the second feed are dual-polarized signals, then the second receive isolation filter can be a dual-mode filter similar in concept to that used with the transmit/receive feed.
Antennas in accordance with the invention can also include additional feeds for communicating with additional sources such as satellites, if desired.
The invention thus simplifies the design and manufacturing of an antenna for satellite communications via dual-polarized signals, and enables the filtering and waveguide elements of the antenna to be made more compact in size and lower in cost compared with prior antennas employing separate filtering of the two components of the dual-polarized signals.